1. Field of the Invention
The present invention relates to methods and apparatus for handling wellbore tubulars. Particularly, the invention relates to an elevator for supporting tubulars for use in wellbore operations. More particularly still, the invention relates to a safety lock for an elevator.
2. Description of the Related Art
The process of running tubulars into a wellbore generally involves the use of an elevator in tandem with a spider. The elevator is typically used to raise or lower the wellbore tubular. As such, the elevator is suspended from a rig hook, which controls the movement of the elevator. A typical elevator comprises two body parts hinged together by a hinge shaft at one end and latched at another end using a latch mechanism. Lift ears may be provided to connect to the bails or other links attached to the rig hook. The elevator includes a bore for receiving the wellbore tubular. The bore is sized such that it is larger than the outer diameter of the tubular, but smaller than the upset area of the tubular. In this respect, the elevator supports the tubular at its upset area during movement.
The spider is typically used for securing the tubular string in the wellbore. A spider generally includes a plurality of slips circumferentially disposed on a “bowl”. The bowl is regarded to be the surfaces on the inner bore of the spider. The exterior surface of the slips and the interior surface of the bowl have opposing engaging surfaces which are inclined and downwardly converging. The inclined surfaces allow the slip to move vertically and radially relative to the bowl. In effect, the inclined surfaces serve as a camming surfaces for engaging the slip with the tubular. Thus, when the weight of the tubular is transferred to the slips, the slips will move downwardly with respect to the bowl. As the slips move downward along the inclined surfaces, the inclined surfaces urge the slips to move radially inward to engage the tubular. In this respect, this feature of the spider is referred to as “self tightening.” Further, the slips are designed to prohibit release of the tubular string until the load is supported by another means.
In the makeup or breakup of wellbore tubulars, the spider remains stationary on the rig floor while securing the tubular string in the wellbore. The elevator positions a tubular section above the tubular string for connection therewith. After completing the connection, the elevator pulls up on the tubular string to release the tubular string from the slips of the spider. The elevator may now lower the tubular string into the wellbore. Before the tubular string is released from the elevator, the spider is allowed to engage the tubular string again to support the tubular string. After the load of the tubular string is transferred back to the spider, the elevator releases the tubular string and continues the tubular makeup process by picking up another tubular section
One of the problems encountered during wellbore operations such as tubing running is the inadvertent release of the tubular section from the elevator. For example, it has been known that the latch mechanism of the elevator may become unlatched due to improper closing or mechanical failure of the latch. Also, the latch mechanism may fail during jarring operations to free a stuck section of the wellbore tubular. The premature release of the tubular section presents a safety hazard to the rig personnel.
There is a need, therefore, for a locking mechanism which will prevent the inadvertent release of the tubular section. There is also a need for a secondary locking mechanism to prevent the inadvertent release of the tubular section if the latch lock fails.